A metal material, such as a galvanized steel sheet material, a steel sheet material and an aluminum material, is corroded through oxidation with oxygen and moisture in the air, and ions or the like contained in moisture. As a measure for preventing the corrosion, there is a method of forming a chromate film by making the metal surface in contact with a treatment solution containing chromium, such as chromic chromate and phosphoric chromate. The film formed by the chromate treatment is excellent in corrosion resistance and adhesiveness to a paint film, but has a problem that the treatment solution therefor contains harmful hexavalent chromium, which causes increase of the time and labor and the cost for the disposal of the treatment solution. Furthermore, the film formed by the treatment contains hexavalent chromium, and thus tends to be prevented from being used.
Accordingly, there have been proposals of an aqueous liquid composition for treating metal surface and a chemical conversion treatment agent that has corrosion resistance equivalent to an conventinal chromate chemical conversion coating and do not contain chromate (see, for example, Patent Documents 1 and 2).
The aqueous liquid composition of Patent Document 1 contains water, (A) a component containing a fluorometallic acid anion in an amount of 0.010 mol/kg or more, (B) a component containing a divalent or tetravalent cation selected from the group consisting of cobalt, magnesium, manganese, zinc, nickel, tin, copper, zirconium, iron and strontium, (C) a component containing at least one anion selected from a phosphorus-containing inorganic oxyanion and a phosphonic acid anion in an amount of 0.015 mol/kg or more in terms of phosphorus, (D) a component containing at least one member selected from the group consisting of a water soluble organic polymer, a water dispersible organic polymer and a polymer-forming resin in an amount of 0.10% or more, and (E) an acid component.
The chemical conversion treatment agent of Patent Document 2 contains zirconium, fluorine and an amino group-containing silane coupling agent, in which the content of zirconium in the chemical conversion treatment agent is from 100 to 700 ppm in terms of metal, and the molar ratio of fluorine to zirconium is from 3.5 to 7.0.
There has been a proposal of a chemical conversion treatment agent that has corrosion resistance equivalent to an conventional chromate chemical conversion coating and does not contain chromate and resin (see, for example, Patent Document 3).
The chemical conversion treatment agent of Patent Document 3 contains as essential components at least one member selected from the group consisting of zirconium, titanium and hafnium, and fluorine, in which the concentration of fluorine is 10% or less in terms of element ratio.